Protein kinases are a class of enzymes that catalyze the transfer of a phosphate group from ATP to a tyrosine, serine, threonine, or histidine residue located on a protein substrate. Protein kinases clearly play a role in normal cell growth. Many of the growth factor receptor proteins have intracellular domains that function as protein kinases and it is through this function that they effect signaling. The interaction of growth factors with their receptors is a necessary event in the normal regulation of cell growth, and the phosphorylation state of substrate proteins often is related to the modulation of cell growth.
The human epidermal growth factor receptor (HER) family consists of four distinct receptor tyrosine kinases referred to as HER1, HER2, HER3, and HER4. These kinases are also referred to as erbB1, erbB2, etc. HER1 is also commonly referred to as the epidermal growth factor receptor (EGFr). With the exception of HER3, these receptors have intrinsic protein kinase activity that is specific for tyrosine residues of phosphoacceptor proteins. The HER kinases are expressed in most epithelial cells as well as tumor cells of epithelial origin. They are also often expressed in tumor cells of mesenchymal origin such as sarcomas or rhabdomyosarcomas. Receptor tyrosine kinases (RTKs) such as HER1 and HER2 are involved in cell proliferation and are associated with diseases such as psoriasis and cancer. Disruption of signal transduction by inhibition of these kinases in target cells is known to have an antiproliferative and therapeutic effect.
The enzymatic activity of receptor tyrosine kinases can be stimulated by either overexpression, or by ligand-mediated dimerization. The formation of homodimers as well as heterodimers has been demonstrated for the HER receptor family. An example of homodimerization is the dimerization of HER1 (EGF receptor) by one of the EGF family of ligands (which includes EGF, transforming growth factor alpha, betacellulin, heparin-binding EGF, and epiregulin). Heterodimerization among the four HER receptor kinases can be promoted by binding to members of the heregulin (also referred to neuregulin) family of ligands. Such heterodimerization, involving HER2 and HER3, or a HER3/HER4 combination, results in a significant stimulation of the tyrosine kinase activity of the receptor dimers even though one of the receptors (HER3) is enzymatically inert. The kinase activity of HER2 has also been shown to be activated by virtue of overexpression of the receptor alone in a variety of cell types. Activation of receptor homodimers and heterodimers results in phosphorylation of tyrosine residues on the receptors and on other intracellular proteins. This is followed by the activation of intracellular signaling pathways such as those involving the microtubule associated protein kinase (MAP kinase) and the phosphatidylinositol 3-kinase (PI3 kinase). Activation of these pathways has been shown to lead to cellular proliferation and the inhibition of apoptosis. Inhibition of HER kinase signaling has been shown to inhibit cell proliferation and survival.
Deregulation of EGF receptors plays a role in the aberrant growth of epithelial cysts in the disease described as polycystic kidney disease [Du, J., Wilson, P. D., Amer. J. Physiol., 269 (2 Pt 1), 487 (1995); Nauta, J., et al., Pediatric Research, 37(6), 755 (1995); Gattone, V. H. et al., Developmental Biology, 169(2), 504 (1995); Wilson, P. D. et al., Eur. J. Cell Biol., 61(1), 131, (1993)]. The compounds of this invention, which inhibit the catalytic function of the EGF receptors, are consequently useful for the treatment of this disease.
The mitogen-activated protein kinase (MAPK) pathway is a major pathway in the cellular signal transduction cascade from growth factors to the cell nucleus. The pathway involves kinases at two levels: MAP kinase kinases (MAPKK), and their substrates MAP (mitogen activated protein) kinases (MAPK). There are different isoforms in the MAP kinase family. [For review, see Seger, R.; Krebs, E. G. FASEB, 9, 726, (1995)]. The compounds of this invention can inhibit the action of one or both of these kinases: MEK, a MAP kinase kinase, and its substrate ERK, a MAP kinase. ERK (extracellular regulated kinases), a p42 MAPK, is found to be essential for cell proliferation and differentiation. Over expression and/or over activation of MEK or ERK has been found to be associated with various human cancers [For example, Sivaraman, V. S. et al., C. C. J. Clin. Invest., 99, 1478 (1997)]. It has been demonstrated that inhibition of MEK prevents activation of ERK and subsequent activation of ERK substrates in cells, resulting in inhibition of cell growth stimulation and reversal of the phenotype of ras-transformed cells [Dudley, D. T. et al., Proc. Nat. Acad. Sci., 92, 7686 (1995)].
Members of the raf family of kinases phosphorylate serine residues on MEK. There are three serine/threonine kinase members of the raf family known as a-raf, b-raf, and c-raf. While mutations in the raf genes are rare in human cancers, c-raf is activated by the ras oncogene which is mutated in a wide number of human tumors. Therefore, inhibition of the kinase activity of c-raf may provide a way to prevent ras mediated tumor growth [Campbell, S. L., Oncogene, 17, 1395 (1998)].
The Src family of cytoplasmic protein tyrosine kinases consists of at least eight members (Src, Fyn, Lyn, Yes, Lck, Fgr, Hck and Blk) that participate in a variety of signaling pathways [Schwartzberg, P. L., Oncogene, 17, 1463 (1998)]. The prototypical member of this tyrosine kinase family is p60src (Src). Src is involved in proliferation and migration responses in many cell types. In limited studies, Src activity has been shown to be elevated in breast, colon (˜90%), pancreatic (>90%) and liver (>90%) tumors. Greatly increased Src activity is also associated with metastasis (>90%) and poor prognosis. Antisense Src message impedes growth of colon tumor cells in nude mice [Staley et al., Cell Growth & Differentation, 8, 269 (1997)], suggesting that Src inhibitors should slow tumor growth. In addition to its role in cell proliferation, Src also acts in stress response pathways, including the hypoxia response. Previous studies have shown that colonic tumor cells genetically engineered to express antisense Src message form tumors demonstrating reduced vascularization in nude mouse models [Ellis, et al., J. Biol. Chem., 273, 1052 (1998)], suggesting that Src inhibitors would be anti-angiogenic as well as anti-proliferative.
Apart from its role in cancer, Src also appears to play a role in osteoporosis. Mice genetically engineered to be deficient in src production were found to exhibit osteopetrosis, the failure to resorb bone [Soriano, P., Cell, 64, 693 (1991); Boyce, B. F., J. Clin. Invest., 90, 1622 (1992)]. This defect was characterized by a lack of osteoclast activity. Since osteoclasts normally express high levels of Src, inhibition of Src kinase activity may be useful in the treatment of osteoporosis [Missbach, M., Bone, 24, 437 (1999)].
In addition to EGFr, there are several other RTKs including FGFr, the receptor for fibroblast growth factor (FGF); flk-1, also known as KDR, and flt-1, the receptors for vascular endothelial growth factor (VEGF); and PDGFr, the receptor for platelet derived growth factor (PDGF). The formation of new blood vessels, a process known as angiogenesis, is essential for tumor growth. Two natural angiogenesis inhibitors, angiostatin and endostatin, dramatically inhibited the growth of a variety of solid tumors. [O'Reilly, M. S., Cell, 79, 315 (1994); O'Reilly, M. S., Nature Medicine, 2, 689 (1996); O'Reilly, M. S., Cell, 88, 277 (1997)]. Since FGF and VEGF are known to stimulate angiogenesis, inhibition of the kinase activity of their receptors should block the angiogenic effects of these growth factors. In addition, the receptor tyrosine kinases tie-1 and tie-2 also play a key role in angiogenesis [Sato, T. N., Nature, 376, 70 (1995)]. Compounds that inhibit the kinase activity of FGFr, flk-1, flt-1, tie-1 or tie-2 may inhibit tumor growth by their effect on angiogenesis.
PDGF is a potent growth factor and chemoattractant for smooth muscle cells (SMCs), and the renarrowing of coronary arteries following angioplasty is due in part to the enhanced proliferation of SMCs in response to increased levels of PDGF. Therefore, compounds that inhibit the kinase activity of PDGFr may be useful in the treatment of restenosis. In addition, since PDGF and PDGFr are overexpressed in several types of human gliomas, small molecules capable of suppressing PDGFr activity have potential utility as anticancer therapeutics [Nister, M., J. Biol. Chem., 266, 16755 (1991); Strawn, L. M., J. Biol. Chem. 269, 21215 (1994)].
In addition, a large number of cytokines participate in the inflammatory response, including IL-1, IL-6, IL-8 and TNF-α. Overproduction of cytokines such as IL-1 and TNF-α are implicated in a wide variety of diseases, including inflammatory bowel disease, rheumatoid arthritis, psoriasis, multiple sclerosis, endotoxin shock, osteoporosis, Alzheimer's disease, and congestive heart failure, among others [Henry et al., Drugs Fut., 24:1345-1354 (1999); Salituro et al., Curr. Med. Chem., 6:807-823 (1999)]. Evidence in human patients indicates that protein antagonists of cytokines are effective in treating chronic inflammatory diseases, such as monoclonal antibody to TNF-α (Enbrel) [Rankin et al., Br. J. Rheumatol., 34:334-342 (1995)], and soluble TNF-α receptor-Fc fusion protein (Etanercept) [Moreland et al., Ann. Intern. Med., 130:478-486 (1999)].
The biosynthesis of TNF-α occurs in many cell types in response to an external stimulus, such as a mitogen, an infectious organism, or trauma. Important mediators of TNF-α production are the mitogen-activated protein (MAP) kinases, and in particular, p38 kinase. These kinases are activated in response to various stress stimuli, including but not limited to proinflammatory cytokines, endotoxin, ultraviolet light, and osmotic shock. Activation of p38 requires dual phosphorylation by upstream MAP kinase kinases (MKK3 and MKK6) on threonine and tyrosine within a Thr-Gly-Tyr motif characteristic of p38 isozymes.
There are four known isoforms of p38, i.e., p38-α, p38β, p38γ, and p38δ. The α and β isoforms are expressed in inflammatory cells and are key mediators of TNF-α production. Inhibiting the p38α and β enzymes in cells results in reduced levels of TNF-α expression. Also, administering p38α and β inhibitors in animal models of inflammatory disease has proven that such inhibitors are effective in treating those diseases. Accordingly, the p38 enzymes serve an important role in inflammatory processes mediated by IL-1 and TNF-α. Compounds that reportedly inhibit p38 kinase and cytokines such as IL-1 and TNF-ααfor use in treating inflammatory diseases are disclosed in the following published international patent applications: WO 00/12497 (quinazoline derivatives as p38 kinase inhibitors); WO 00/56738 (pyridine and pyrimidine derivatives for the same purpose); WO 00/12497 (discusses the relationship between p38 kinase inhibitors); and WO 00/12074 (piperazine and piperidine compounds useful as p38 inhibitors).
In summary, the tight regulation of signal transduction normally exerted by the array of kinase enzymes is often lost in malignant cells. Compounds which modulate these kinases are thus highly desirable for the treatment of disorders associated with aberrant cellular proliferation. Moreover, compounds which modulate the cytokines associated with the inflammatory response are highly desirable for the treatment of inflammatory disorders.